A. Field of the Invention
This invention relates to novel foam compositions and methods of using such novel compositions as fracturing fluids and well bore cleaning fluids. In particular, the invention relates to multipurpose aqueous foaming compositions which may be used in any aqueous system.
It is well known that subterranean hydrocarbon-bearing formations may be hydraulically fractured to improve production of same. In the usual processes, various liquids, such as crude oil, kerosene, water, acids, water/alcohol mixtures, brines, foams and the like, are injected into the hydrocarbon formation via an injection well or producing well. By increasing the pressure on the fluid, the formation is placed under hydraulic stress in order to fracture the formation and thereby form channels which more easily allow hydrocarbons to migrate to the surface via the production well.
The fracturing fluid must have a viscosity which is low enough to permit adequate penetration of the formation but, at the same time, sufficiently high that excessive leak-off of the fluid to the formation does not occur. The fracturing fluid must also have sufficient body that it will carry propping agents to all parts of the fractured formation.
Foams meet the various criteria necessary for an efficient fracturing fluid. In the past, however, it has been necessary to tailor the foam to the particular environment encountered in the various formations which are to be fractured. Formations are frequently treated with a variety of fluids prior to and during extended hydrocarbon recovery methods as described above. Thus, a formation frequently has been exposed to fresh water or brines, or the formation may have been acidized with acids such as hydrochloric acid, or, in order to avoid the excessive use of water, such as in clay-containing formations, a water/alcohol mixture is frequently used so that the clay does not swell and close off the formation pores necessary for hydrocarbon migration. Each of the various types of fluids which have been used to assist hydrocarbon production present special problems in the formulation of a foam fracturing fluid. Thus, it has been necessary to formulate specifically tailored foams for injection into formtions which have been treated with fresh water, brines, acids, water/alcohol mixtures and the like. Foaming agents (i.e. surfactants) which may work efficiently in an acid environment frequently do poorly in fresh water. Further, typical aqueous foaming agents will not foam in the presence of alcohols, which require special surfactants.
Accordingly, an object of the present invention is to provide a multipurpose foamable composition, and the foam generated therefrom for use in aqueous media, which will provide a stable foam for fracturing and well cleaning when formulated with fresh water, brine, aqueous acids and water/alcohol mixtures.
Another object of the invention is to provide a foamable fracturing and well cleaning surfactant composition which forms a stable foam in a variety of aqueous media at reduced loading rates.
A further object of the invention is to provide methods for fracturing hydrocarbon formations and cleaning wells by treatment of a formation or well with a foam prepared from a multipurpose foamable fluid.
Further objects of this invention will be apparent from the disclosure herein.
B. Prior Art
The use of foams, generated from aerated foamable fluids, in the fracturing of hydrocarbon formations and for use in well bore cleanout is well known in the art, however, the prior art does not teach the preparation of a multipurpose aqueous foamer which may be used in environments which have previously been treated with, or contain, fresh water, brine, acids, alcohol/water mixtures or the like. For example:
U.S. Pat. No. 3,463,231 describes the circulation of fluids as well cleaning agents.
U.S. Pat. No. 3,572,440 discloses the use of aqueous foamable fluids containing acids for use in cleaning well bores and to facilitate stimulation of the producing zone of the well as by cleaning it.
U.S. Pat. No. 3,937,283 describes the hydraulic fracturing of hydrocarbon formations using a foamable fluid prepared from a liquid base, e.g., water, brines, acid, oil, hydrocarbon condensates and the like. A surface active foaming agent such as anionic, cationic or non-ionic materials or mixtures thereof, depending on the environment, are used together with a gas.
U.S. Pat. No. 3,980,136 describes compositions and methods for fracturing well formations using a foam having a specified quality. The foam is prepared by adding a surface active agent to a slurry of sand in water and introducing thereto a large amount of gas.
U.S. Pat. No. 4,404,112 describes the use of silicon-induced hydrocarbon foam mixtures suitable for use in well stimulation.